1. Field of the Invention
The present invention relates to a technology for appropriately detecting edge of an image.
2. Description of the Related Art
Images taken by a camera and raster illustrations etc. include various objects, so that it is quite difficult to carry out identification of the objects in a computer, or it is required for the computer to execute high-load operations. Meanwhile, it is required to perform identification of objects in the image information in various situations such as detection of a suspicious figure by separating the figure from background by real-time analysis in a security camera, or processing for enhancing edge (outline) of the respective objects in an image of blurring. Therefore, various edge detection technologies for identifying objects in the image are provided. Specifically, the edge is a portion where precipitous change in brightness in the image is found, and Canny edge detection utilizing brightness gradient etc, and differentiation based edge detection are well known.
Moreover, since the respective pixel values in the image taken by the camera are determined by integrating color of object and color of light, it is preferable to carry out the edge detection only by the color of object excluding effects of the lights such as unevenly lighting. An example of estimating only the light from the integration value of the color of object and the color of light indicated by the image data includes image blurring. In Japanese Patent No. 3909604, when a coefficient, calculated by normalizing a brightness value of a target pixel C for edge determination and a brightness value in peripheral image of blurring (an average brightness value in a block configured by peripheral pixels of the pixel C), is more than or equal to 1, it is determined that the pixel C is an edge.